Catalytic gas synthesis apparatus

ABSTRACT

The present invention is generally directed to an improved process and apparatus for the production of gaseous products such as ammonia by catalytic, exothermic gaseous reactions and is specifically directed to an improved process which utilizes a gas-phase catalytic reaction of nitrogen and hydrogen for the synthesis of ammonia. This improved process for the production of ammonia utilizes an ammonia converter apparatus designed to comprise at least two catalyst stages and a reheat exchanger so arranged as to provide indirect heat exchange of the gaseous effluent from the last reactor catalyst stage with the effluent from at least one other reactor catalyst stage having a higher temperature level in order to reheat the effluent from the last reactor catalyst stage prior to exiting the reactor vessel, thereby facilitating higher level heat recovery from the reactor effluent.

This is a division of application, Ser. No. 691,398, filed Jan. 14,1985, now U.S. Pat. No. 4,637,918, which is a division of applicationSer. No. 472,998, filed Mar. 7, 1983, now U.S. Pat. No. 4,518,574,issued May 21, 1985.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to process and apparatus useful in catalytic gassynthesis reactions, and more specifically to process and apparatususeful in the synthesis of ammonia.

2. Description of the Prior Art

Generally, the manufacture of ammonia consists of preparing an ammoniasynthesis gas from a nitrogen source, usually air, and from a hydrogensource, which is conventionally either coal, petroleum fractions, ornatural gases. In the preparation of ammonia synthesis gas from naturalgases, for example, a raw (that is, hydrogen-rich) synthesis gas isformed by first removing gaseous contaminants such as sulfur from thenatural gas by hydrogenation and adsorption, and then by reforming thecontaminant-free gas. The carbon monoxide in the raw synthesis gas isconverted to carbon dioxide and additional hydrogen in one or more shiftconversion vessels, and the carbon dioxide is removed by scrubbing.Further treatment of the raw synthesis gas by methanation may be used toremove additional carbon dioxide and carbon monoxide from the hydrogenrich gas, resulting subsequently in an ammonia synthesis gas containingapproximately three parts of hydrogen and one part of nitrogen, that is,the 3:1 stoichiometric ratio of hydrogen to nitrogen in ammonia, plussmall amounts of inerts such as methane, argon and helium. The ammoniasynthesis gas is then converted to ammonia by passing the ammoniasynthesis gas over a catalytic surface based on metallic iron(conventionally magnetite) which has been promoted with other metallicoxddes, and allowing the ammonia to be synthesized according to thefollowing exothermic reaction:

    N.sub.2 +3H.sub.2 →2NH.sub.3

Ammonia synthesis, as is characteristic of exothermic chemicalreactions, suffers from a competition between equilibrium and kinetics.The equilibrium conversion of hydrogen and nitrogen to ammonia isfavored by low temperatures. However, the forward reaction rate toammonia strongly increases with temperature. This leads to an optimalreactor temperature profile which starts relatively high, in order toget reaction rates as fast as possible while still far away fromequilibrium, and which is then allowed to gradually fall along thereaction path in the reactor to improve equilibrium as the reactionprogresses. Unfortunately, by definition, exothermic reactions give offheat, and hence the temperature tends to rise as the ammonia synthesisprogresses, prematurely stopping the reaction when an unfavorableequilibrium is approached.

A number of solutions to this problem have evolved in the form ofparticular ammonia synthesis reactor designs. In modern, large scaleammonia plants (600 to 2,000 tons of ammonia per day) two general typespredominate. Both use two or more adiabatic stages with cooling betweenstages in order to move away from equilibrium after each stage. Thebasic difference between the types of reactors is in the cooling method.In the first, a direct contact quench is used with a portion ofunreacted cold feed being brought into contact with the heated effluentwhich is desired to be cooled. In the second type of reactor, indirectheat exchange is used to cool the desired gas streams. The former typeof reactor is simpler in construction but is not as efficient becausepart of the feed by-passes all but the last stage in order to effect thedesired cooling within the reactor. The optimum operation of eithertype, which can be readily calculated by one skilled in the art, employsa declining sequence of reaction stage outlet temperatures. This isillustrated by FIG. 7 of U.S. Pat. No. 4,181,701.

Since the reaction is exothermic, the heat of reaction can theoreticallybe recovered as useful waste heat. Conventionally, the waste heat isrecovered from the reactor effluent, which, as previously mentioned, isrelatively cold, since the last reaction stage has the lowest outlettemperature of the several beds within the reactor. Waste heat recoverybetween stages is known in the art and is disclosed in such referencesas U.S. Pat. Nos. 3,721,532; 4,101,281, 4,180,543, and 4,181,701 and incommonly assigned co-pending application Ser. No. 414,523 filed Sept. 2,1982, now abandoned (the disclosure of which application is herebyincorporated by reference). However, the reported schemes either requirethe expense of a second reactor vessel, or bear the risk of poisoning ofthe catalyst or of explosive and thereby safety-related problems ingenerating steam for removal of the reaction heat by use of steamgeneration coils located inside the reactor vessel, which generallycontains a reduced catalyst that is potentially violently reactive withwater or steam at the elevated temperatures which are used.

SUMMARY OF THE INVENTION

The present invention is generally directed to an improved process andapparatus for the production of gaseous products such as ammonia bycatalytic, exothermic gaseous reactions and is specifically directed toan improved process which utilizes a gas-phase catalytic reaction ofnitrogen and hydrogen for the synthesis of ammonia. This improvedprocess for the production of ammonia utilizes an ammonia converterapparatus designed to comprise at least two catalyst beds so arranged asto provide indirect heat exchange of the gaseous effluent from the lastreactor catalyst bed with the effluent from at least one other reactorcatalyst bed having a higher temperature level in order to reheat theeffluent from the last reactor catalyst bed prior to exiting the reactorvessel, thereby facilitating higher level heat recovery from the ammoniaconverter effluent.

The present invention is particularly advantageous in providing a methodand apparatus suitable for retrofit of more active catalyst intoexisting exothermic reaction equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective process schematic flowsheet of a prior artexothermic catalytic synthesis process.

FIG. 2 is a perspective process schematic flowsheet of one embodiment ofan improved exothermic catalytic synthesis process and reactor of thepresent invention, employing two heat exchangers and two catalyst beds.

FIG. 3 is a perspective process schematic flowsheet of anotherembodiment of the improved exothermic catalytic synthesis process andreactor, of the present invention, employing two catalyst beds, a singleheat exchanger and direct contact quenching.

FIG. 4 is a perspective process schematic flowsheet of yet anotherembodiment of the improved exothermic catalytic synthesis process andreactor of the present invention, employing three catalyst beds, and areheat exchanger in combination with one or more interbed exchangersand/or direct contact quenching.

FIG. 5 is a sectional elevation flow diagram of a first embodiment ofthe reactor vessel of the present invention.

FIG. 6 is a sectional elevation flow diagram of a second embodiment ofthe reactor vessel of this invention.

FIG. 7 is a sectional elevation flow diagram of a third embodiment ofthe reactor vessel of the present invention.

FIG. 8 is a sectional elevation flow diagram of a fourth embodiment ofthe reactor vessel of the present invention.

FIG. 9 is a sectional elevation flow diagram of a fifth embodiment ofthe reactor vessel of the present invention.

FIG. 10 is a sectional elevation flow diagram of a sixth embodiment ofthe reactor vessel of the present invention.

FIG. 11 is a sectional elevation flow diagram of a seventh embodiment ofthe reactor vessel of the present invention employing quench gas forcooling of reheat exchanger effluent prior to the second catalyst bed.

DETAILED DE$CRIPTION OF THE INVENTION

The apparatus of this invention will be described below particularly inrelation to its use in the synthesis of ammonia. However, it will beunderstood that the apparatus is useful in any catalytic, exothermic gassynthesis reaction.

Referring to FIG. 1, a typical prior art operating sequence isillustrated for an intercooled, two-stage catalytic reactor 10. Thereactor vessel 10 contains a "catalyst basket" including two catalystbeds 2 and 6, and interbed heat exchanger 4 and lower heat exchanger 8.A portion of the feed gas 15 to the reactor is passed via conduit 1 tolower heat exchanger 8, and a separate portion via conduit 3 to interbedheat exchanger 4 for indirect cooling in these heat exchangers of gasstreams 6b and 2b, respectively. If desired, a portion or all of eitherstreams 1, 3 or 5 can be employed for annular cooling of the pressureshell of the reactor prior to introduction of these streams into therespective reactor components, that is, heat exchanger 8, heat exchanger4, and first catalyst bed 2, respectively. When the desired gas productis ammonia, the gas feedstream will typically comprise a mixture of N₂and H₂ (generally in a mole ratio of about 3:1, that is from about 2.5:1to about 3.5:1) plus small amounts of inerts such as Ar and He. Catalystbeds 2 and 6 are controlled at their kinetically optimal temperaturesvia the two heat exchangers. Waste heat recovery from reactor effluent 9is via a high pressure steam generator 16, located immediatelydownstream of reactor 10. By use of this steam generator, generally allof the available waste heat can be recovered from the effluent as highpressure steam (e.g., 900-2000 psig). Downstream of this boiler 16 is afeed/effluent heat exchanger 14 that preheats the converter feed 12.This exchanger 14 is provided with a bypass conduit 23, controlled bymeans of a bypass control valve 25, which can be used to control reactorfeed temperature, if necessary. Valve 25 is generally fully closed,since this results in the maximum waste heat recovery. If thefeed/effluent exchanger 14 is bypassed, more heat is thrown away to awater-cooled exchanger 18, which is located immediately downstream offeed-effluent exchanger 14.

In the embodiment shown in FIG. 1, devices 4 and 8 comprise heatexchangers. The prior art, however, has also proposed the replacement ofexchanger 4 with direct contact quenching using a portion of the cooler,unreacted gas feed.

In the event a more active catalyst is retrofitted into reactor 10, itbecomes possible to slow down the ammonia synthesis gas compressor andthereby decrease feed gas pressure and the total flow rate through thereactor. Due to the enhanced activity of the catalyst, the conversionper pass rises so that it is still possible to maintain a constantammonia production rate even though the total flow rate through thereactor decreases. Also, again due to the enhanced catalyst activity,the kinetically optimum bed temperatures drop significantly and with thehigher conversion per pass, the overall temperature rise across thereactor increases.

As a result of a retrofit of such a more active catalyst into reactor10, the reduced flow rate means that recovery of all of the waste heatin high pressure boiler 16 (which has a roughly constant gas outlettemperature due to a cold-end heat transfer pinch, i.e., a smalltemperature driving force between the stream to be heated and theexiting heating fluid) would require an increase in the inlettemperature to the boiler, which would require a corresponding increasein the temperature of outlet gas 9 from reactor 10. However, the outlettemperature from second catalyst bed 6 has dropped substantially at thesame time. This, in turn, means that it would be desired to do less heattransfer in the lower heat exchanger 8, and perhaps to completely bypasslower heat exchanger 8, effectively making the reactor outlettemperature equal to the outlet temperature of catalyst bed 6. However,if the new retrofit catalyst is sufficiently more active, this wouldstill not achieve the objective of recovering all the waste heat in highpressure boiler 16, since the temperature of stream 6b would be lessthan the required temperature of stream 9.

Thus, with a retrofit of a substantially more active catalyst (forexample, a retrofit catalyst having at least 20 percent, and preferablyat least 50 to 200 percent or more, activity enhancement relative to thecatalyst for which the reactor system was designed), the prior artprocesses require one to either open bypass valve 25 on thefeed/effluent heat exchanger 14 and throw valuable waste heat away tocooling water exchanger 18, or to install a lower pressure boiler 24,downstream of high pressure boiler 16, to recover the heat at lowertemperatures, e.g., as medium pressure steam (500-900 psig). The formerapproach, opening valve 25, throws away a large amount of the heataltogether, whereas the latter approach, requiring use of a lowerpressure boiler 24, degrades part of the high pressure steam previouslyproduced in boiler 16 to a lower pressure (and hence less valuable)steam, and requires investment for the new piece of equipmentrepresenting new boiler 24.

The extent to which such a retrofit of more active catalyst presents aloss of heat recovery efficiency can be seen by reference to ComparativeExample 1, presented below.

In accordance with the improved process of this invention, thetemperature of the effluent from the last reaction stage in anexothermic reactor, having two or more catalyst stages arranged forsequential gas flow therethrough, is increased by reheating at least aportion, and preferably substantially all, of this effluent gas in areheat exchanger by indirect heat exchange with the effluent from thefirst or other reactor stage. FIGS. 2 and 3 illustrate this broadconcept using an intercooled, two-stage catalytic reactor, and aquench-type reactor, respctively, and FIG. 4 illustrates this conceptusing a three-stage catalytic reactor. However, it will be understoodthat our concept is broadly applicable to designs using at least twocatalyst stages, and to reactor designs using indirect heat exchangeand/or quench for interstage cooling of the effluent of one or morecatalyst stages, although less reheating can be done in quench-typedesigns, since flows through the catalyst stages are unequal.

As used herein, the term "catalyst stage" is intended to refer to acatalyst bed within the reactor whose gaseous effluent is either cooledand passed to another catalyst bed within the reactor or, in the case ofthe last catalyst bed, is withdrawn as product gas from the reactor asdescribed herein.

Reference is now made to FIGS. 2-4 which illustrate the reactor systemof the process of this invention and wherein similar numbers refer tothe same or similar elements.

Referring now to FIG. 2, one embodiment of the reactor system of theprocess of this invention is schematically illustrated. In reactor 110,there is provided first catalyst bed 102, interbed heat exchangers 104and 108, and second catalyst bed 106. Reactor feed 112 is passed tofeed/effluent exchanger 114 wherein the feed gas is preheated. Thethus-heated feed gas 115 is then split into two portions. A firstportion is passed as stream 119 to reactor 110 for feed to firstcatalyst bed 102. A second portion is passed as stream 118a to interbedheat exchanger 108 within reactor 110 for heating by heat exchange withgas stream 105 which is passed thereto from second exchanger 104, whichcomprises the reheat exchanger. The thus-heated feedstream 120 iswithdrawn and combined with the remaining feed gas 119 for combined feed121 to first catalyst bed 102. An effluent gas 103 is withdrawn from bed102 and passed to reheat exchanger 104 wherein this gas effluent heatsat least a portion of gas effluent 107 withdrawn from second catalystbed 106 prior to withdrawing the second catalyst bed effluent fromreactor 110. The partially cooled first catalyst bed effluent 105 iswithdrawn from reheat exchanger 104, and passed to interbed heatexchanger 108 as explained above for heating of feed gas stream 118a,and the further cooled first bed effluent gas 109 is then passed tosecond catalyst bed 106. The effluent gas 107 from the second catalystbed is heated in reheat exchanger 104 by first catalyst bed effluent gas103 and is then withdrawn from reactor 110 via conduit 124 for wasteheat recovery in steam generator 122. Thus, boiler 122 can comprise ahigh pressure boiler adapted to produce high pressure steam (e.g.,900-2000 psig). If desired, a lower pressure boiler 128 can be installeddownstream of high pressure boiler 122 in order to recover waste heat atlower temperatures, for example, to produce medium pressure steam(500-900 psig). Following waste heat recovery, the reactor effluent ispassed to feed/effluent exchanger 114 and is then withdrawn from theprocess via conduit 117 and can be passed to a cooling water exchanger(not shown) for further cooling. As illustrated, feed/effluent exchanger114 is provided with bypass loop 123 which is controlled by means ofvalve 125 in order to control the temperature of the feed 115 to reactor110.

If desired, a portion or all of streams 118a and/or 119 can be employedfor annular cooling of the pressure shell of the reactor prior to theintroduction of these streams into the respective reactor components,that is, heat exchanger 108 and first catalyst bed 102, respectively.

If desired for temperature control, a portion of stream 103 can beby-passed around reheat exchanger 104 and recombined with stream 105downstream of exchanger 104. Alternatively, a portion of the secondcatalyst bed effluent gas 107 can be by-passed around exchanger 104 andrecombined with product gas stream 124.

Referring to FIG. 3, another embodiment of the reactor system of theprocess of this invention is schematically illustrated which correspondsto the embodiment of FIG. 2, except that the second interbed heatexchanger is replaced by use of a direct contact quench. In thisembodiment, the partially cooled first catalyst bed effluent gas iscontacted with a portion of the cooler, unreacted feed gas prior tointroduction of this gas into the second catalyst bed. In FIG. 3,reactor 110 is provided with first catalyst bed 102, interbed heatexchanger 104 (which comprises the reheat exchanger) and second catalystbed 106. Reactor feed 115, after being preheated in feed/effluentexchanger 114 (not shown) is split into two portions. A first portion ispassed as stream 119 to reactor 110 for feed to first catalyst bed 102.A second portion is passed as stream 118b to be employed for directcontact quenching of the partially cooled first catalyst bed effluentgas stream 105 which is then passed as feed to second catalyst bed 106.An effluent gas 103 is withdrawn from first bed 102 and passed to reheatexchanger 104 wherein this gas effluent heats at least a portion of thegas effluent 107 withdrawn from second catalyst bed 106, prior towithdrawing the second catalyst bed effluent gas from reactor 110. Thepartially cooled first catalyst bed effluent 105 is withdrawn fromexchanger 104 and further cooled to the desired temperature by contactwith quench-gas stream 118b to form a combined mixture 109 which is thenpassed as feed to second catalyst bed 106. The second catalyst bedeffluent gas heated in reheat exchanger 104 is withdrawn therefrom viaconduit 124 for waste heat recovery in steam generator 122 as describedabove. If desired, a portion or all of feed gas streams 119 and/or 118bcan be employed for annular cooling of the pressure shell of the reactorprior to the introduction of this stream into first catalyst bed 102.

As indicated above, the concept of this invention is equally applicableto the use of more than two catalytic beds/stages. FIG. 4 illustrates areactor 110 employing three catalyst beds 102, 106 and 133. In thisembodiment, preheated, fresh gas feed 115 is divided into threeportions. A first portion 119 is passed as a part of the gas feed tofirst catalyst bed 102. A second portion is introduced to first interbedheat exchanger 108 via conduit 118a, and a third portion is introducedvia conduit 131a to second interbed heat exchanger 130. The thus-heatedportion of heating fluid passed to exchanger 130 is withdrawn therefromvia conduit 132 and combined with the remaining portion of the heatedsynthesis gas in conduit 120 for feed to first catalyst bed 102, asdescribed above.

The gaseous effluent from first bed 102 is passed as stream 103 toreheat exchanger 104 wherein at least a portion of the gaseous effluentfrom the last catalyst bed, third catalyst bed 133 in the embodiment ofFIG. 4, is heated prior to withdrawing gas product 124 from reactor 110.The partially cooled first catalyst bed effluent is then further cooledby means of first exchanger 108 via indirect heat exchange with gas feed118a (or, optionally, by direct contact quenching in lieu of exchanger108, using a portion of the cooler, gas feed introduced, for example, asstream 118b). The resting cooled first bed effluent gas 109 is thenpassed as feed to second catalyst bed 106. After the further reactionwhich takes place in bed 106, the second bed effluent 107 is cooled insecond interbed exchanger 130 with the third gas feed portion 131a (or,optionally by direct contact quenching in lieu of exchanger 130, using aportion of the cooler, gas feed introduced, for example, as stream131b). The resulting cooled second catalyst bed effluent gas is thenwithdrawn as stream 135 for feed to third catalyst bed 133. As describedabove, at least a portion of the gaseous effluent from third bed 133 ispassed as stream 134 to reheat exchanger 104. Product gas is withdrawnvia conduit 124 from reactor 110 and can then be passed to heatrecovery, as described above with respect to FIG. 2. As with thepreceding figures, if desired, a portion or all of streams 119, 118a,118b, 131a and/or 131b can be employed for annular cooling of thepressure shell of the reactor 110 prior to the introduction of thesestreams into the respective reactor components.

While not illustrated, it will be apparent that the partially cooledfirst catalyst bed effluent 105 withdrawn from reheat exchanger 104 canbe directly introduced as feed into second catalyst bed 106 and that, inthis embodiment, no interbed heat exchanger 108 or interbed quenchingvia conduit 118b is employed for further cooling of the gas in stream105 prior to its introduction into second bed 106. In this embodiment,therefore, the feed to first catalyst bed 102 will comprise feed gasportion 119 and feed gas portion 132, (where heat exchanger 130 isemployed for cooling of the second catalyst bed effluent gas 107).

The embodiments illustrated in FIGS. 2-4 are, of course, not limiting ofthis invention, and reactors containing more than three catalyst stagescan also be employed.

As will be illustrated in FIGS. 5-11, the heat exchangers used in theprocess of this invention can comprise baffled tubular heat exchangers.However, these heat exchangers can be of any suitable type, such as forinstance plate-fin exchangers, close tube exchangers and the like. Also,while the catalyst beds are preferably each arranged for radial flow ofgases therethrough, it will be understood that our invention is notlimited thereby and that one or more (or all) of the catalyst beds cancomprise (1) longitudinal flow beds in which the gas flows through thebeds in a direction which is substantially parallel to the verticallongitudinal axis of the reactor, or (2) transverse flow beds in whichthe gas flows through the beds in a direction which is transverse to themajor direction of gas flow through a horizontal reactor, such as areillustrated in G. P. Eschenbrenner and G. A. Wagner, "A New HighCapacity Ammonia Converter", vol. 14, Ammonia Plant Safety, 51-56,(Chem. Eng. Progr. Techn. Manual, AICHE, 1972).

As is the case in FIG. 2, in the embodiments of FIGS. 3 and 4, it willbe understood that one or more of exchangers 104, 108 and 130, whereapplicable, can be by-passed by selected amounts of the heating fluidpassed thereto, in order to provide the desired temperature control.Furthermore, a portion of the last catalyst bed effluent gas 107 and 134in FIGS. 3 and 4, respectively, can be by-passed around reheat exchanger104 for temperature control.

Referring now to FIG. 5, one embodiment of the reactor vessel of thepresent invention is illustrated which is generally indicated at 200. Asillustrated, reactor 200 comprises a cylindrical pressure-resistantshell 238 having an upper circular closure member 201 provided with acentrally-located aperture 202 through which gas feed enters the vesselinto a gas-header space 203 defined by inner surface 233 of closuremember 201 and upper closure plate 231 of reactor cartridge 236. At thelower-most end of reactor shell 238 is located a concentric tubularassembly comprising an outer tube 204 for removal of gas product fromthe reactor and an inner tube 206 for passage of additional quantitiesof gas feed to the reactor, both tubes 204 and 206 being preferablypositioned coaxially with the longitudinal axis of reactor shell 238.Reactor cartridge 236 is sized so as to provide an annular coolingchannel 234 between the inner vertical surfaces 232 of reactor shell 238and the outer vertical surfaces of cartridge 236. In addition, reactorcartridge 236 is sized so that the lower-most portion of reactorcartridge 236, comprising surfaces 280, defines (1) a lower gas space278 beneath surfaces 280 and above the inner surface of lower portion282 of shell 238, (2) a second gas space 276 above surfaces 280 andbelow lower catalyst plate 274 of lower catalyst bed 260, and (3) a gasopening 284, annularly arranged about the assembly of tubes 204 and 206,to allow feed gas to pass into second gas space 276. Positioned withinreactor cartridge 236, are upper catalyst bed 210, baffled reheatexchanger 240, baffled interbed heat exchanger 250 and lower catalystbed 260, all arranged in an annular manner about the cylindrical axis ofpressure shell 238. The upper surface of annular catalyst bed 210 isdefined by a circular closure plate 212, and forms a second header space223 (beneath upper cartridge closure plate 231) which communicates withinterior passageway 207 of inner tube 206 to permit a first portion ofthe synthesis gas feed, which is introduced into feed tube 206, to passupwardly from the lower portion of shell 238 to second header space 223and thence radially, outwardly above upper closure plate 212 to annulargas passageway 228, which is formed by the outer cylindrical sheet 224of catalyst bed 210 and the adjacent inner vertical surfaces of reactorcartridge 236 to permit gases to pass downwardly to and through opening229 which is provided about the circumference of cylindrical sheet 224and thereby to enter catalyst bed 210.

The second portion of the synthesis gas feed, introduced into aperture202, passes downwardly to, and then outwardly through, gas header space203 and then downwardly into annular cooling channel 234 to provideannular cooling of pressure shell 238. The feed gas passes out of thelower portion of annular channel 234 into lower gas space 278 and thenupwardly through opening 284 into second gas space 276 and then intoannular gas space 272, which is defined by the outer cylindrical sheet262 and the inner wall of reactor cartridge 236. In annular space 272,tne gases flow past lower catalyst bed 260 and into the shell side ofinterbed heat exchanger 250 by way of opening 256. In exchanger 250, thegas feed is caused to flow a tortuous path by means of baffles 258 andis heated further by indirect heat exchange with gaseous effluent fromfirst catalyst bed 210 (which has been first partially cooled in reheatexchanger 240, as described in more detail below). The thus-heated feedgas is withdrawn from exchanger 250 and passes upwardly through annularspace 228, along the outer vertical walls 224 of exchanger 240, to enterfirst catalyst bed 210 by way of opening 229, together with theremaining feed gas which is passed downwardly to annular space 228 fromsecond header space 223, as described above.

Catalyst bed 210 comprises lower catalyst plate 226, which supports thecatalyst, and circular closure plate 212, and is provided with an outergas permeable wall 220 (which defines an annular gas distributionchannel 222 in order to permit gases entering opening 229 to distributewithin catalyst bed 210) and inner gas permeable wall 214. (Gaspermeable walls in this invention can be illustrated by metal sheetsand/or screens having suitable perforations to permit gas passage whileavoiding spillage of catalyst particles from the catalyst beds.) Walls214 and 220 are at their lower ends secured to catalyst plate 226.

Gases exiting catalyst bed 210 pass through permeable wall 214 and enterannularly-shaped gas withdrawal channel 216 defined by gas permeablewall 214 and the adjacent portions of outer cylindrical surface 246 ofgas inlet tube 206. Gases exiting upper catalyst bed 210 pass frompassageway 216 into first baffled heat exchanger 240 via gas space 230defined by lower catalyst plate 226 and the upper tubesheet 247 ofexchanger 240. This gas effluent enters tubes 249 of exchanger 240 forheating of the gaseous effluent from second catalyst bed 260, which iscaused to flow a tortuous path through exchanger 240 by means of baffles248. Gases are passed from exchanger 240 into exchanger 250, and in theembodiment shown, the two exchangers employ common gas passage tubes249. In the lower portion of tubes 249, in interbed exchanger 250, thegas effluent from catalyst bed 210 is additionally cooled by means of aportion of gas feed which is passed thereto in order to effect a finalstage of cooling of this upper catalyst bed effluent to the desired feedtemperature to lower catalyst bed 260. The gases exit tubes 249 ofinterbed exchanger 250 into gas space 257 defined by lower tubesheet 253of interbed heat exchanger 250 and circular closure plate 264 of secondcatalyst bed 260 and are then passed downwardly into annular gasdistribution channel 268 (defined by outer cylindrical sheet 262 andouter gas permeable wall 270), through the outer gas permeable wall 270,and radially, inwardly through catalyst bed 260, through inner gaspermeable wall 266 and thence as gas effluent from second catalyst bed260, into annular gas withdrawal channel 241 defined by innercylindrical sheet 242 and inner gas permeable wall 266, along bed 260,and second inner cylindrical sheet 254, along interbed heat exchanger250. The resulting second catalyst bed gas effluent passes upwardlythrough annular gas passage 241, after bypassing interbed heat exchanger250, into reheat exchanger 240, for heating by indirect heat exchangewith the gas effluent from first catalyst bed 210. The thus-heatedeffluent gas is withdrawn from the shell side of reheat exchanger 240via annular product passage 244, defined by inner cylindrical sheet 242and outer cylindrical surface 246 of gas feed tube 206, and is thendischarged from reactor 200 as product via product tube 204.

In operation, a first portion of the synthesis gas feed is introducedvia feed tube 206 into the lower portion of reactor 200. This feed gaspasses upwardly through feed passage 207 to second upper header space223 from which the gas is passed outwardly, radially to and thendownwardly along, inner annular channel 228 for introduction via opening229 as a portion of the gas feed to first catalyst bed 210. A secondportion of the gas feed to reactor 200 is then introduced via aperture202 into upper header space 203 and thence to annular cooling channel234 for cooling of pressure shell 238. These cooling gases are withdrawnfrom cooling channel 234 at the lower portion thereof into successivegas spaces 278 and 276 and are then introduced into inner gas channel272 for passage to the shell side of interbed exchanger 250. Inexchanger 250, this portion of the feed gas is heated by indirect heatexchange with partially cooled first catalyst bed effluent gas and thethus-heated feed gases are withdrawn from the shell side of exchanger250 into the lower portion of inner annular gas channel 228 for passageto opening 229 as the remaining portion of the gas feed to firstcatalyst bed 210.

Gas product is collected from catalyst bed 210 into gas withdrawalchannel 216 and then passed downwardly into gas space 230 forintroduction into tubes 249 of reheat exchanger 240, wherein the firstcatalyst bed effluent gas heats the effluent gas from the secondcatalyst bed and from which the first bed effluent gases, after beingpartially cooled, are passed to the tube side 249 of exchanger 250 forliberation of additional heat therefrom by the above-described heatingof the annular cooling gases introduced to the shell side of exchanger250. Further cooled first catalyst bed effluent gas is passed fromexchanger 250 into gas space 257 and thence into gas distributionchannel 268 for feed to second catalyst bed 260. The further reacted gasis withdrawn from catalyst bed 260 into inner gas withdrawal channel241, and the second catalyst bed effluent gas is then passed to theshell side of exchanger 240 for heating with first catalyst bed effluentgas as described above. The thus-heated second catalyst bed effluent gasis withdrawn from the shell side of exchanger 240 into gas productchannel 244 and ultimately withdrawn from reactor 200 via product tube204.

Referring now to FIG. 6, another embodiment of the reactor vessel of thepresent invention is illustrated which is generally indicated at 300. Asillustrated, reactor 300 comprises a cylindrical pressure-resistantshell 338 having an upper circular closure member 301 provided with acentrally-located aperture 302 through which gas feed enters the vesselinto gas header space 303 defined by inner surface 333 of closure member301 and upper cartridge closure plate 331 of reactor cartridge 336. Atthe lower-most end of reactor shell 338 is located a concentric tubularassembly comprising an outer tube 304 for removal of gas product fromthe reactor and an inner tube 306 for passage of additional quantitiesof gas feed to the reactor, both tubes 304 and 306 being arranged in anassembly, preferably coaxially with the cylindrical reactor. Reactorcartridge 336 is sized so as to provide an annular cooling channel 334between the inner vertical surfaces 332 of reactor shell 338 and theouter vertical surfaces of cartridge 336. In addition, reactor cartridge336 is sized so that the lower-most portion of reactor cartridge 336,comprising surfaces 380, defines (1) a lower gas space 378 beneathsurfaces 380 and above the inner surface of lower portion 382 of shell338, (2) a second gas space 376 above surfaces 380 and below lowercatalyst plate 326 of lower catalyst bed 310, and (3) a gas opening 384annularly arranged about the assembly of tubes 304 and 306, to allowfeed gas to pass into second gas space 376 and then upwardly into innerannular gas space 372 for passage to first catalyst bed 310 via gasopening 329.

Within reactor cartridge 336 is positioned inner baffled cartridge 362provided with upper closure member 313 and cylindrical vertical sheet362. Upper closure member 313 of inner cartridge 362 is positioned belowclosure member 331 of outer reactor cartridge 336 in order to provide asecond upper gas header space 335, which communicates centrally disposedgas passage 307 with inner annular gas channel 372, which is defined by,and located between, the cylindrical sheets defining the verticalsurfaces of reactor cartridge 336 and inner baffled cartridge 362.

Substantially annular shaped upper catalyst bed 360, which comprises thesecond catalyst bed for treatment of the process stream, is providedwith a circular upper catalyst plate 364 and a circular lower catalystplate 374, which acts to support the catalyst within bed 360. The outercircumference of annular shaped catalyst bed 360 is defined by theadjacent vertical surfaces of baffled cartridge 362 and innercylindrical sheet 342. In addition, catalyst bed 360 is provided withcylindrical outer gas permeable wall 370 and cylindrical inner gaspermeable wall 366, which walls are secured to support plate 374. Outergas permeable wall 370 defines an annular gas distribution channel 368along the adjacent portion of the outer cylindrical sheet defining thevertical surface of baffled inner cartridge 362, and inner gas permeablewall 366 and inner cylindrical sheet 342 define gas withdrawal channel352 which communicates with a lower gas space 373 positioned beneathlower catalyst plate 374 and upper baffle surface 375 of outer annularshaped, baffled reheat exchanger 340. Gas distribution channel 368communicates with a third gas header space 357 which is itself definedby the upper surfaces of upper catalyst plate 364 and circular closuremember 313 of baffled cartridge 362 to permit gases to pass outwardly,radially, through gas header space 357 to and then downwardly along gasdistribution channel 368 for passage radially, inwardly, throughcatalyst bed 360 and ultimate withdrawal therefrom through permeablewall 366 into gas withdrawal channel 352, from which the withdrawn gasesare passed outwardly through lower header space 373 and into the shellside of heat exchanger 340 wherein the second catalyst bed effluent gasis caused to flow a tortuous path therethrough by means of baffles 358and wherein this effluent gas is heated by indirect heat exchange withthe hotter effluent gas from first catalyst bed 310, to be described inmore detail below. The thus-heated second catalyst bed effluent gas iswithdrawn from the shell side of the exchanger 340 via annular productpassage 308 (which is defined by outer wall 318 of feed tube 306 andouter surface 317 of product withdrawal tube 304) and ultimately removedfrom reactor shell 338 at the lower portion thereof via product tube304.

Substantially annular shaped lower catalyst bed 310, which issubstantially annularly shaped and comprises the first catalyst bed fortreatment of the process stream in the apparatus of FIG. 6, is providedwith upper circular catalyst plate 312 and lower catalyst plate 326,which acts to support the catalyst housed in bed 310. Lower catalyst bed310 is provided with outer gas permeable wall 320 and inner gaspermeable wall 314, each of which are substantially cylindrical in shapeand which are secured to support plate 326. An annular gas distributionchannel 328 is defined by outer gas permeable wall 320 and the adjacentportions of the outer cylindrical sheet which in turn defines thevertical surface of inner baffled cartridge 362, and in which opening329 is provided, preferably at the lower portion thereof, to extendabout the circumference of catalyst bed 310 in order to permit feedgases to pass into gas distribution channel 328 for passage radially,inwardly, through bed 310. Inner gas permeable wall 314 defines gaswithdrawal channel 351 along the adjacent portions of the outercylindrical surface 317 of product withdrawal tube 304. Gas withdrawalchannel 351 receives the gas effluent from first catalyst bed 310 andpasses these gases upwardly into gas space 386 defined by catalyst plate312 and lower tubesheet 385 of reheat exchanger 340. From gas space 386the first catalyst bed effluent gases enter tubes 349 for heating, byindirect heat exchange, of the gas effluent from second catalyst bed360, as described above. The partially cooled first bed effluent gasesare withdrawn from tubes 349 and are then passed into the shell side ofbaffled interbed heat exchanger 350 in which they are caused to flow atortuous path by means of baffles 387 and in which these gases arefurther cooled by indirect heat exchange with fresh synthesis gas whichis passed to the tube side of exchanger 350 from gas feed passage 315 towhich this gas feed is introduced via feed tube 306. The further cooledeffluent from catalyst bed 310 is withdrawn from the shell side ofexchanger 350 via annular space 344 which is defined by the innercylindrical sheet 342 of catalyst bed 360 and the outer cylindricalsurfaces of center tube 346, which in turn communicates the tube side ofheat exchanger 350 with second upper header space 335. The thuspartially cooled first catalyst bed effluent is passed upwardly throughupper annular space 344 to third header space 357 and then radially,outwardly, to gas distribution channel 368 and then downwardly as feedinto second catalyst bed 360.

The partially heated feed gases withdrawn from tubes 345 of heatexchanger 350 are passed upwardly through tube 346 into gas space 307and then into, and radially, outwardly through, second gas header space335 from which the gases are passed downwardly into inner annularchannel 372 in which the gases flow past upper catalyst bed 360 andreheat exchanger 340 and into opening 329 as feed to first catalyst bed310.

A second portion of the synthesis gas feed to the reactor is introducedvia aperture 302 into upper header space 303 from which it flowsoutwardly to annular cooling channel 334 and then into lower headerspace 376 and inner annular channel 372 as a portion of the feed tofirst catalyst bed, 310 via opening 329.

Referring now to FIG. 7, yet another embodiment of the reactor vessel ofthis invention, indicated generally at 400, is illustrated, whichcomprises a cylindrical pressure-resistant shell 438 which is providedwith upper circular closure member 405 having a centrally positionedaperture 402 to permit gas feed to reactor 400. Within pressure shell438 is positioned reactor cartridge 465 which is provided with uppercircular closure member 403 defining upper header space 406 positionedbeneath inner surface 404 of upper closure member 405. The outer,substantially-cylindrical vertical surfaces of reactor cartridge 465define an annular gas cooling channel 461 within pressure shell 438adjacent to the inner cylindrical surfaces 463 thereof. Reactorcartridge 465 is so sized as to provide a lower gas header space 484above the lowermost portion 486 of pressure shell 438 and the lowersurfaces 482 of reactor cartridge 465. Surfaces 482 also define gaspassageway 494 which communicates with lower header space 484 and asecond lower header space 480 positioned above surfaces 482 and beneathcatalyst plate 478. In the lower portion 486 of pressure shell 438 ispositioned the tubular assembly comprising an outer product tube 488 andan inner gas supply tube 490, which are preferably arranged coaxiallyabout the vertical cylindrical axis of pressure shell 438 and whichprovide an annular gas space 492 between tubes 488 and 490 to permitproduct gases to be withdrawn from the shell side of reheat exchanger440, as will be described in more detail below. Gas supply tube 490 isadapted to pass feed gas upwardly through the reactor and to supply thisgas to the tube side 410 of upper exchanger 450, as will also bedescribed in more detail below.

Within reactor cartridge 465 there is provided substantially cylindricalinner baffled cartridge 418 having upper closure plate 414 and catalystsupport plate 478, and housing, in ascending order from the lowerportions thereof above catalyst plate 478: first catalyst bed 431; abaffled, tubular reheat exchanger (indicated generally at 440); thirdcatalyst bed 421; and second catalyst bed 411 in which is positioned,along the center axis thereof, a baffled tubular interbed heat exchanger(indicated generally at 450). Catalyst beds 431, 421 and 411 areannularly shaped and are positioned about the central axis of gas feedtube 490, which passes gas feed from the lower portion of reactor 400,upwardly through the innermost portions of the reactor to provide gasfeed to the tube side 410 of upper, centrally positioned, interbed heatexchanger 450. Inner baffled cartridge 418 is sized so as to define asecond upper header space 401 above plate 414 and below plate 403 and todefine an inner annular gas channel 424 between the vertical outersurfaces of cartridge 418 and the adjacent portions of the verticalsurfaces of reactor cartridge 465. Gas channel 424 communicates withsecond lower header space 480 and second upper header space 401 topermit gas feed to be passed to first catalyst bed 431, via opening 476,downwardly from second header space 401 and upwardly from lower gasspace 480.

First, second and third catalyst beds 431, 411, and 421, respectively,and reheat exchanger 440 are substantially annular in shape and arepositioned about the longitudinal axis of pressure shell 438. Firstcatalyst bed 431 is defined by inner cylindrical sheet 468 and theadjacent cylindrical vertical surfaces of inner baffled cartridge 418,and is situated above catalyst plate 478 which acts to support thecatalyst in bed 431. Bed 431 is also provided with outer gas permeablewall 474 and inner gas permeable wall 470, which are secured to supportplate 478 and which are so positioned as to form annular gasdistribution channel 472 and annular gas withdrawal channel 466 adjacentto the respective vertical sheets 418 and 468.

Similarly, third catalyst bed 421 is supported upon catalyst supportplate 455 and is provided with an upper catalyst plate 430, outer gaspermeable wall 448 and inner gas permeable wall 444, and annular gasdistribution channel 420 and annular gas withdrawal channel 446 alongthe respective adjacent portions of the vertical cylindrical walls ofinner baffled cartridge 418 and inner cylindrical sheet 442. Walls 444and 448 are secured to support plate 455.

Second catalyst bed 411, comprising the upper catalyst bed in reactor400, is provided with outer gas permeable wall 422 and inner gaspermeable wall 426 and is supported by plate 430 to which walls 422 and426 are secured. The upper portions of catalyst bed 411 are defined bycircular closure plate 414. Annular gas distribution channel 416 isprovided between inner gas permeable wall 426 and outer cylindricalsheet 427 defining the outer surfaces of upper exchanger 450, in orderto permit gas feed to second catalyst bed 411 from exchanger 450. Thegases fed to bed 411 pass therethrough radially, outwardly and exitthrough outer gas permeable wall 422 into annular gas channel 420 forfeed downwardly into third catalyst bed 421, through which the gas ispassed radially, inwardly.

Reheat exchanger 440 is provided with tubes 496 which communicate withlower gas space 462, positioned below tubesheet 467 and above closureplate 464, and with a second gas space 456, positioned above tubesheet460 and beneath a circular channel guide 454 to permit gases exitingfrom first catalyst bed 431 via gas withdrawal channel 466 to pass intogas space 462 and then upwardly through the tube side 496 of reheatexchanger 440 for indirect heat exchange with and heating of the productgases withdrawn via gas withdrawal channel 446 from third catalyst bed421. Reheat exchanger 440 is also provided with baffles 458, which causethe product gases entering the shell side of exchanger 440 via gas space452 to flow a tortuous path through exchanger 440 for indirect heatexchange with, and heating by, the effluent gases from first catalystbed 431. The product gases which are thus heated are withdrawn fromexchanger 440 via annular product passage 492, which is positionedbetween gas product tube 488 and the outer surfaces of gas feed tube490. These product gases are withdrawn from reactor 400 via product tube488. An annular gas passage 445 is provided between the innercylindrical sheet 442 of bed 421 and the adjacent portions of gas feedtube walls 497 and communicates gas space 456 with the shell side ofexchanger 450 to permit gases to pass from tubes 496 of reheat exchanger440 to interbed exchanger 450, as will be described in more detailbelow.

Upper, interbed exchanger 450 is centrally positioned about thelongitudinal axis of reactor shell 438, and is provided with tubes 410for communication of gas feed from gas feed passage 498 within gas feedtube 490 and second header space 401 and for heating of this gas feedtherein by indirect heat exchange with the partially cooled gas effluentfrom first catalyst bed 431 which is passed thereto via annular gaspassage 445. Baffles 499 within upper exchanger 450 provide a tortuouspassage for the partially cooled first catalyst bed effluent gas to flowtherethrough for indirect heat exchange with, and heating of, thisportion of the gas feed to the reactor.

In operation, a first portion of the gas feed is introduced via heattube 490 and passed upwardly through center feed passage 498 to upperexchanger 450 in which this gas is heated with partially cooled firstcatalyst bed effluent which is introduced to the shell side of exchanger450 via inner annular gas passage 445. The thus-heated gas feed iswithdrawn from tube side 410 of exchanger 450 into second header space401 and passed outwardly through header space 401 to, and downwardlyalong, inner annular gas channel 424 to the lower portion of innerbaffled cartridge 418 to opening 476 (which is positioned about thecircumference of the cylindrical cartridge 418 for feed of this gas togas passage 472) and thence radially, inwardly, through first catalystbed 431. The thus-reacted gases are then withdrawn to the tube side 496of reheat exchanger 440 for heating of the effluent gases from thirdcatalyst bed 421 and for subsequent passage to the shell side of upperheat exchanger 450 for preheating of gas feed as described above. Fromthe shell side of upper exchanger 450 the first bed effluent gases arepassed to annular gas distribution channel 416 and thence radially,outwardly through catalyst bed 411 wherein they are further reacted.Product gases exit second catalyst bed 411 into annular gas channel 420and are then introduced to third catalyst bed 421 through which thesegases flow radially, inwardly. The product gases from third catalyst bed421 are withdrawn via gas channel 446 and gas space 452 to the shellside of reheat exchanger 440 for heating of these gases before beingwithdrawn as product via tube 488.

A second portion of the gas feed is introduced via upper aperture 402 toupper header space 406 in which the gases flow radially outwardly to,and then downwardly along, annular cooling channel 461, after which thegases enter, sequentially, lower header space 484 and second lowerheader space 480 for ultimate passage to the lower portion of inner gaschannel 424 as part of the feed to first catalyst bed 431.

It will be recognized that the three catalyst beds in the embodiment ofFIG. 7 are actually representative of two catalyst stages sinceessentially no heat removal for temperature control is intentionallyaccomplished between second catalyst bed 411 and third catalyst bed 421,so that beds 411 and 421 can be viewed as comprising one catalyst stage.FIG. 7, therefore, illustrates that interbed heat removal is notrequired between each and every catalyst bed in accordance with thisinvention where, for example, dictates of construction require that asingle catalyst stage be separated into two or more catalyst beds.

Referring now to FIG. 8, another embodiment of the apparatus of thisinvention (indicated generally at 500) is illustrated which comprisescylindrical pressure-resistant shell 512 having upper closure member 506provided with a centrally positioned gas feed/product assembly having anouter gas feed tube 504 and an inner gas product tube 502. Tubes 502 and504 are preferably positioned concentrically about the verticalcylindrical axis of pressure shell 512 and provide annular gas passage509 which communicates with upper header space 505. Within pressureshell 512 there is positioned cylindrical reactor cartridge 526 havingan upper closure plate 501 and a lower support plate 560. Cartridge 526is sized so as to provide (1) annular gas cooling channel 514 along theadjacent vertical cylindrical inner walls 510 of pressure shell 512, (2)upper header space 505 above upper closure plate 501 and below innersurface 503 of circular closure member 506, and (3) lower header space564 below lower support plate 560 and above lower inner surface 562 ofpressure shell 512.

At the lower portion of pressure shell 512 there is positioned a secondgas feed tube 566, preferably located along the vertical cylindricalaxis of pressure shell 512 for introducing feed gases into uppercatalyst bed 508, as will be described in more detail below. Withinreactor cartridge 526 there is positioned, in ascending order from thelower portions thereof: second catalyst bed 552; interbed heat exchanger550; and first catalyst bed 508, which is positioned about the verticalcylindrical axis of pressure shell 512 and within an annular-shapedreheat exchanger 540.

Second catalyst bed 552 is annularly shaped and is situated uponcatalyst support plate 558 which acts to support the catalyst within bed552, and which is positioned to form second lower gas space 568 belowplate 558 and above support plate 560 of reactor cartridge 526. Bed 552is also provided with inner gas permeable wall 548, inner cylindricalsheet 546, outer gas permeable wall 556 and upper closure plate 574.Walls 548 and 556 are secured to support plate 558. Annular gaswithdrawal channel 553 is provided between inner gas permeable walls 548and inner cylindrical sheet 546. Annular gas distribution channel 554 isprovided between outer gas permeable walls 556 and the adjacent portionof outer cylindrical sheet 538. Outer cylindrical sheet 538 extendsupwardly to also define the outer walls of exchanger 550 and to providesecond annular gas passage 536 between sheet 538 and the adjacentportions of the inner vertical cylindrical surfaces of reactor cartridge526. Gases exiting catalyst bed 552 are collected in inner gas channel553 and flow downwardly, through gas space 568, and then upwardly intoannular gas space 536 to the shell side of reheat exchanger 540, as willbe described in more detail below. Inner cylindrical sheet 546 is itselfpositioned to provide inner annular gas passage 570 between sheet 546and the outer wall 572 of second gas feed tube 566. Inner annular gaschannel 570 communicates with lower header space 564 and the shell sideof centrally positioned interbed heat exchanger 550 for further heating,as will also be described in more detail below.

Heat exchanger 550 comprises gas tubes 543 which are adapted to receiveheating fluid from gas space 532, flow baffles 576, upper tubesheet 541and lower tubesheet 542. Exchanger 550 is adapted to receive feed gasfrom inner annular gas passage 570 into the shell side of exchanger 550wherein this gas is caused to flow a tortuous path about tubes 543 forheating by indirect heat exchange with partially cooled gas effluentfrom catalyst bed 508 which is passed to tubes 543. A gas space 544 isprovided between tubesheet 542 and closure plate 574 to receive gasesexiting tubes 543 and to pass these gases to gas distribution channel554 for feed to second catalyst bed 552. A second gas space 532 isprovided above tubesheet 541 of exchanger 550 to receive the partiallycooled first catalyst bed effluent from the tube side 584 of reheatexchanger 540 and for passage of this gas to the tube side 543 ofexchanger 550. The heated feed gas is withdrawn from the shell side ofexchanger 550 into center gas space 580 wherein this heated feed gas iscombined with the second portion of the feed gas which is passedupwardly through gas feed tube 566 from the lower portion of pressureshell 512. This combined feed gas stream then enters intermediate tube534 which connects gas space 580 with a center gas distribution passage516 for feed of these gases to first catalyst bed 508.

First catalyst bed 508 is annularly shaped and is provided with upperclosure plate 592, outer gas permeable wall 520 and inner gas permeablewall 518, which are secured to a support plate 528. A centrallypositioned gas distribution channel 516 is provided inside bed 508 fordistribution of feed gas from intermediate tube 534 radially, outwardly,through catalyst bed 508, and annular gas withdrawal channel 522 isprovided between outer gas permeable walls 520 and the inner verticalsheet 524 of reheat exchanger 540 to collect gas effluent from first bed508 for introduction to reheat exchanger 540.

Baffled reheat exchanger 540 is annularly shaped and positioned aboutthe longitudinal axis of pressure shell 512 and surrounds first catalystbed 508. First exchanger 540 is provided with gas tubes 584, flowbaffles 586 and lower tubesheet 530 and is adapted to receive firstcatalyst bed effluent gas from gas withdrawal channel 522 into an uppergas space 590, positioned above tubesheet 531 and beneath upper closureplate 592 which extends to enjoin a closure channel surface 591.Exchanger 540 is also adapted to receive into its shell side, from thelower portion of exchanger 540, second catalyst bed effluent gas whichis passed thereto from inner annular gas passage 536 and which is causedto flow a tortuous path through exchanger 540 by means of baffles 586for heating by indirect heat exchange with the first catalyst bedeffluent gas which flows through tubes 584. The thus-heated secondcatalyst bed effluent gas is withdrawn from the shell side of exchanger540 into upper header space 507 and is then withdrawn from reactor 500via product tube 502. Partially cooled first catalyst bed effluent gasis withdrawn from tubes 584 and passed to gas space 532 for introductioninto the tube side of second exchanger 550, as described above.

In operation, a first portion of the gas feed is passed via feed tube504 to provide annular cooling gas in channel 514 to cool reactor shell512. This annular cooling gas passes from cooling channel 514 to gasspaces 564 and inner gas channel 570 and enters the shell side of heatexchanger 550 in which the gas feed is further heated by indirect heatexchange with a partially cooled first catalyst bed effluent, afterwhich the further heated feed gas is combined in zone 580 with a secondportion of the gas feed, which is passed upwardly to zone 580 via gasfeed tube 566, and then introduced via tube 534 to feed passage 516 forfeed to first catalyst bed 508. The gas passes through bed 508 radially,outwardly, and the reacted gas is withdrawn as gas effluent into channel522 and then passed via gas space 590 into heat exchange tubes 584 forfinal heating of the gas effluent from second catalyst bed 552.

The partially cooled first catalyst bed effluent gas withdrawn into gasspace 532 from reheat exchanger 540 is then passed to tubes 543 ofinterbed exchanger 550 for the preheating of the annular gas feed, andthe further cooled first catalyst bed effluent is collected in gas space544 and passed to gas distribution channel 554 for feed, radially,inwardly, to second catalyst bed 552. Product gases are withdrawn frombed 552 into gas withdrawal channel 553 and then passed via gas space568 and gas channel 536 to the shell side of reheat exchanger 540 forfinal heating and for ultimate withdrawal from reactor 500 via gasheader space 507 and gas product tube 502 as described above.

Referring now to FIG. 9, yet another embodiment of the reactor apparatusof this invention (indicated generally at 600) is illustrated whichcomprises a cylindrical pressure-resistant shell 616 which is providedwith an upper circular closure member 601 having a centrally positionedaperture 602 communicating with gas header space 605 located below innersurfaces 607 of closure member 601. Within pressure shell 616 ispositioned: (1) in the upper portion thereof, first reactor cartridge622 (which houses first catalyst bed 614 and baffled reheat exchanger640); and (2) in the lower portion thereof, second reactor cartridge 654(which houses second catalyst bed 672). A baffled, interbed heatexchanger 650 is positioned in pressure shell 616 between first reactorcartridge 622 and second reactor cartridge 654 and is adapted to providegaseous communication there between as will be described in more detailbelow.

First reactor cartridge 622 is sized so as to provide gas header space605 thereabove and to provide first annular cooling channel 626 betweencartridge 622 and the adjacent portions of the inner cylindricalvertical surfaces 618 of pressure shell 616. Similarly, second reactorcartridge 654 is sized so as to provide lower header space 660, beneathcatalyst support plate 658 and above the lower inner surface 661 oflower portion 662 of pressure shell 616, and a second annular coolingchannel 656 between cartridge 654 and the adjacent portions of the innervertical cylindrical surfaces 618 of reactor shell 616. First annularcooling channel 626 is adapted to receive gases from upper header space605 for feed to first catalyst bed 614 and is separated from gas channel656 by means of circumferential seal baffle 638.

Reheat exchanger 640 is positioned within first catalyst bed 614, whichis annularly shaped, and catalyst bed 614 and exchanger 640 are eacharranged about the vertical cylindrical axis of pressure shell 616.Catalyst bed 614 is supported upon catalyst support plate 684 and isenclosed along its upper surface by closure member 603. Bed 614 isprovided with outer gas permeable wall 624 and inner gas permeable wall632, which are secured to support plate 684. An annular gas distributionchannel 620 is defined between outer gas permeable wall 624 and theadjacent portions of the cylindrical sheet forming the inner verticalsurfaces of first reactor cartridge 622. An inner annular gas withdrawalchannel 628, is defined between inner gas permeable wall 632 and innercylindrical sheet 630, which comprises the outer vertical wall ofexchanger 640. Gas withdrawal channel 628 is adapted to pass theeffluent gas from first catalyst bed 614 to the shell side of reheatexchanger 640 for indirect heat exchange with, and heating of, theeffluent gases from the second catalyst bed 672, as will be described inmore detail below.

Exchanger 640 comprises tubes 608, flow baffles 686, upper closure sheet604 and lower concave baffle 634. Upper closure sheet 604 provides a gasspace 606 to collect gases exiting from the tube side 608 for passage tothe upper portion of product tube 668 for withdrawal of the productgases from the reactor via longitudinal gas passage 674 as shown. Lowerconcave baffle 634 defines conical gas space 682 which is adapted toreceive the gaseous effluent from second catalyst bed 672 via annulargas passage 643 for introduction of these gases to tubes 608. Baffles686 cause the first catalyst bed effluent gas to flow a tortuous paththrough exchanger 640. Exchanger 640 is adapted to permit the partiallycooled first catalyst bed effluent gases to be withdrawn from the shellside of exchanger 640 into lower gas space 680 (which is located belowcatalyst support plate 684 and concave baffle 634 and above uppertubesheet 636 of second exchanger 650) for passage into tubes 678 ofsecond exchanger 650.

Interbed exchanger 650 comprises tubes 678, flow baffles 653, uppertubesheet 636 and lower tubesheet 644. Exchanger 650 is sized so as toprovide an inner annular gas passage 643 along the adjacent portions ofouter wall 676 of gas product tube 668, to provide gaseous communicationbetween inner withdrawal channel 641 of second bed 672 and conical gasspace 682 of reheat exchanger 640. Tubesheet 644 and upper closure plate646 of catalyst bed 672 define gas space 642 for collection of gasesfrom tubes 678 and for passage of these gases to gas distributionchannel 652 for feed to second catalyst bed 672. Tubes 678 communicategas space 680 with gas space 642 for passage of partially cooled firstcatalyst bed effluent gas through exchanger 650. Exchanger 650 isadapted to receive annular cooling gases into the shell side thereof,and baffles 653 are arranged so as to cause the annular cooling gas toflow a tortuous path about the external surfaces of tubes 678 forheating by indirect heat exchange with the hotter gases in tubes 678.

In second catalyst cartridge 654 there is provided second catalyst bed672 which is substantially annular in shape and is positioned about thevertical cylindrical axis of pressure shell 616. Bed 672 is supported bycatalyst support plate 658 and is provided with outer gas permeable wall648 and inner gas permeable wall 651, each of which is secured tosupport plate 658. A closure member 646 defines the upper bounds ofcatalyst bed 672. A substantially annular shaped gas distributionchannel 652 is provided between outer gas permeable wall 648 and theadjacent vertical cylindrical sheet which defines the vertical surfacesof second catalyst cartridge 654 to permit gases to be distributed asfeed to catalyst bed 672 along the length thereof. A gas collectionchannel 641 is also provided as a substantially annular shaped channelbetween inner gas permeable wall 651 and the adjacent portions of thecylindrical outer surfaces 676 of gas product tube 668. Gas collectionchannel 641 communicates with annular gas passage 643 for passage of thesecond bed effluent gas to the tube side of reheat exchanger 640 forheating by indirect heat exchange with the effluent gases from firstcatalyst bed 614.

Lower portion 662 of pressure shell 616 is provided with concentricallypositioned inner gas product tube 668 and outer gas feed tube 666, eachof which are positioned about the vertical cylindrical axis of pressureshell 616. Outer gas feed tube 666 defines an annular shaped gas feedchannel 670 which communicates with lower header space 660 which in turncommunicates with second annular cooling gas channel 656 for cooling ofthe adjacent lower portions of pressure shell 616 and for feeding ofthese annular gases to the shell side of interbed exchanger 650, whereinthe gases are further heated by indirect heat exchange with partiallycooled first catalyst bed effluent gas, as described above.

In operation, a first portion of the gas feed is passed via aperture 602into upper header space 605 and thence outwardly to, and downwardlyalong, annular cooling channel 626 to the lower portion of gasdistribution channel 620 at which point these annular cooling gases arecombined with gases exiting the shell side of exchanger 650 for feed tofirst catalyst bed 614. A second portion of the gas feed is passed viafeed tube 666 and annular gas passage 670 to lower header space 660 andthence to second annular cooling channel 656, followed by introductioninto the shell side of exchanger 650 for further heating by contact withpartially cooled first catalyst bed effluent gases. The thus-heatedannular cooling gases are withdrawn from the shell side of exchanger 650and combined with the remaining gas feed in gas distribution channel620, as described above, for feed to first catalyst bed 614.

The gas effluent exiting first catalyst bed 614 is collected in gaschannel 628 and passed to the shell side of reheat exchanger 640 forheating of the product gases withdrawn from second catalyst bed 672. Thepartially cooled first catalyst bed effluent gases are passed to thelower gas space 680 and then to the tube side of exchanger 650 forpreheating of the annular cooling gases passed thereto from secondannular cooling channel 656, as described above. The first catalyst bedeffluent gases are withdrawn from tubes 678 of exchanger 650 and thenpassed via gas space 642 to gas distribution channel 652 for feed tosecond catalyst bed 672.

Product gases withdrawn from second catalyst bed 672 are collected inchannel 641 and passed upwardly via inner annular gas passage 643 andgas space 682 to tubes 608 of reheat exchanger 640 for heating byindirect heat exchange with first catalyst bed effluent gas. The thusheated second catalyst bed effluent gases are withdrawn from the reactorvia product tube 668.

Referring now to FIG. 10, yet another embodiment of the apparatus ofthis invention is illustrated which is indicated generally at 700.Reactor 700 comprises substantially cylindrical pressure-resistant shell708 which is provided with a circular upper closure member 705 having acentrally positioned tubular assembly comprising an inner gas producttube 702 and an outer gas feed tube 704, each of which are positionedabout the vertical cylindrical axis of pressure shell 708. Outer gasfeed tube 704 defines an annular shaped gas channel 784 whichcommunicates with an upper header space 782 provided below the innersurface 780 of upper closure member 705.

Within pressure shell 708 is positioned: (1) in the upper portionthereof, first reactor cartridge 720 (which houses first catalyst bed774 and baffled reheat exchanger 740) and (2) in the lower portionthereof, second reactor cartridge 746 (which houses second catalyst bed766). A baffled interbed heat exchanger 750 is positioned in pressureshell 708 between first reactor cartridge 720 and second reactorcartridge 746 and is adapted to provide gaseous communicationtherebetween as will be described in more detail below.

First reactor cartridge 720 is sized so as to provide gas header space782 thereabove and to provide first annular cooling channel 722 betweencartridge 720 and the adjacent portions of the inner cylindricalvertical surfaces 724 of pressure shell 708. Similarly, second reactorcartridge 746 is sized so as to provide lower header space 756, beneathcatalyst support plate 764 and above the lower inner surface 758 oflower portion 760 of pressure shell 708, and a second annular coolingchannel 744 between cartridge 746 and the adjacent portions of the innervertical cylindrical surfaces 724 of reactor shell 708. First annularcooling channel 722 is adapted to receive gases from upper header space782 for feed to first catalyst bed 774 and is separated from gas channel744 by means of circumferential seal baffle 736.

Reheat exchanger 740 is positioned within first catalyst bed 774, whichis annularly shaped, and catalyst bed 774 and exchanger 740 are eacharranged about the vertical cylindrical axis of pressure shell 708.Catalyst bed 774 is supported upon catalyst support plate 726 and isenclosed along its upper surface by closure member 776. Bed 774 isprovided with outer gas permeable wall 716 and inner gas permeable wall710, each of which is secured to support plate 726. An annular gasdistribution channel 718 is defined between outer gas permeable wall 716and the adjacent portions of the cylindrical sheet forming the innervertical surfaces of first reactor cartridge 720. An inner annular gaswithdrawal channel 714, is defined between inner gas permeable wall 710and inner cylindrical sheet 712, which comprises the outer verticalwalls of first exchanger 740. Gas withdrawal channel 714 is adapted topass the effluent gas from first catalyst bed 774 to the shell side ofexchanger 740 for indirect heat exchange with, and heating of, theeffluent gases from the second catalyst bed 766, as will be described inmore detail below.

Reheat exchanger 740 comprises tubes 706, flow baffles 772, upperclosure sheet 771 and lower concave baffle 773. Upper closure sheet 771provides a gas space 778 to collect gases exiting from the tube side 706for passage to the lower portion of product tube 702 for withdrawal ofthe product gases from the reactor as shown. Lower concave baffle 773defines lower conical gas space 781 which is adapted to receive thegaseous effluent from second catalyst bed 766 via longitudinal gaspassage 754 for introduction of these gases to tubes 706. Baffles 772cause the first catalyst bed effluent gas to flow a tortuous paththrough exchanger 740. Exchanger 740 is adapted to permit the partiallycooled first catalyst bed effluent gases to be withdrawn from the shellside of exchanger 740 into lower gas space 728 (which is located belowcatalyst support plate 726 and concave baffle 773 and above uppertubesheet 735 of interbed exchanger 750) for passage into tubes 734 ofexchanger 750.

Interbed exchanger 750 comprises tubes 734, flow baffles 768, uppertubesheet 735 and lower tubesheet 743. Exchanger 750 is annular shapedand positioned about inner longitudinal gas passage 754. Tubesheet 743and upper closure plate 742 of catalyst bed 766 define gas space 738 forcollection of gases from tubes 734 and for passage of these gases to gasdistribution channel 753 for feed to second catalyst bed 766. Tubes 734communicate gas space 728 with gas space 738 for passage of partiallycooled first catalyst bed effluent gas through exchanger 750. Exchanger750 is adapted to receive annular cooling gases into the shell sidethereof, and baffles 768 are arranged so as to cause the annular coolinggas to flow a tortuous path about the external surfaces of tubes 734 forheating by indirect heat exchange with the hotter gases in tubes 734.

In second catalyst cartridge 746 there is provided second catalyst bed766 which is substantially annular in shape and is positioned about thevertical cylindrical axis of pressure shell 708. Bed 766 is providedwith outer gas permeable wall 748 and inner gas permeable wall 752, eachof which is secured to catalyst support plate 764. A closure member 742defines the upper bounds of catalyst bed 766. A substantially annularshaped gas distribution channel 753 is provided between outer gaspermeable wall 748 and the adjacent vertical cylindrical sheet whichdefines the vertical surfaces of second catalyst cartridge 746 to permitgases to be distributed as feed to catalyst bed 766 along the lengththereof. A substantially cylindrically shaped, longitudinal gas passage754 is also provided within bed 766 and is defined by inner gaspermeable wall 752.

A centrally positioned aperture 762 is provided in lower portion 760 ofpressure shell 708 to permit gas feed to be introduced into lower headerspace 756.

In operation, a first portion of a gas feed is passed via aperture 762into lower header space 756 and thence outwardly to, and upwardly along,annular cooling channel 744 to the shell side of exchanger 750 whereinthese annular gases are further heated by indirect heat exchange withpartially cooled first catalyst bed effluent gas which is passed throughtubes 734. The thus heated annular gases are withdrawn from the shellside of exchanger 750 and combined with the remaining portion of thefeed gas for passage to annular distribution channel 718 as feed alongthe outer portion of first catalyst bed 774. A second portion of the gasfeed is passed via feed tube 704 and annular gas passage 784 to upperheader space 782 and thence to upper annular cooling channel 722, fromwhich this portion of the annular feed gases are combined with the gasesexiting the shell side of exchanger 750 and fed, as described above, tofirst first catalyst bed 774.

The first catalyst bed effluent gas is withdrawn via gas collectionchannel 714 and passed to the shell side of exchanger 740 wherein thefirst catalyst bed gas effluent imparts at least a portion of its heatto second catalyst bed effluent gas which is passed through tubes 706 ofexchanger 740. Thereafter, the partially cooled first catalyst bedeffluent gas is introduced to tubes 734 of exchanger 750, as describedabove, from which these gases are withdrawn into gas space 738 anddistributed along gas channel 753 as radial, inward feed to secondcatalyst bed 766 for additional reaction. The product gases withdrawnfrom second bed 766 into centrally positioned, longitudinal gas passage754 and upwardly past exchanger 750 into tubes 706 of exchanger 740 forfinal heating of the second bed effluent gas as described above. Thethus heated product gases are withdrawn from reactor 700 via producttube 702.

Referring now to FIG. 11, yet another embodiment of the apparatus ofthis invention (indicated generally at 800), based on a quenchconfiguration, is illustrated which comprises a cylindricalpressure-resistant shell 834 which is provided with an upper circularclosure member 810 having a centrally positioned tubular assemblycomprising concentrically arranged tubes 802 and 804 communicating withgas header spaces 814 and 822, respectively, as will be described inmore detail below. Within reactor shell 834 is positioned substantiallycylindrical reactor cartridge 826 which is provided with upper closuremember 816 and lower surface 882. Reactor cartridge 826 is sized so asto provide upper gas header space 814 above upper closure member 816 andbelow inner surfaces 812 of reactor closure member 810 and to providelower gas header space 876 in the lower portion of reactor 800 aboveinner surfaces 881 of reactor shell 834 and below lower surfaces 882 ofreactor cartridge 826. In addition, reactor cartridge 826 is sized so asto provide annular cooling channel 828 between the vertical surfaces ofcartridge 826 and the adjacent portions of the inner verticalcylindrical surfaces 832 of reactor shell 834. Annular cooling channel828 provides gaseous communication between upper gas header space 814and lower gas header space 876 to permit cooling gases to passtherethrough for cooling of surfaces 832. Within reactor cartridge 826is positioned: (1) in the upper portion thereof, first catalyst bed 830;(2) in the lower portion thereof, second catalyst bed 890; and (3) in anintermediate position between beds 830 and 890, reheat exchanger 840,which is adapted to provide gaseous communication between said catalystbeds, as will be described in more detail below.

Upper catalyst bed 830 comprises substantially circular, upper closuremember 824, outer gas permeable wall 820 and inner gas permeable wall836. Walls 820 and 836 are each secured to support plate 838. Upperclosure member 824 is positioned so as to define an inner gas headerspace 822 adapted to provide gaseous communication with gas feed tube804 and an annular shaped gas distribution channel 821 which is definedby, and positioned between, outer gas permeable wall 820 and theadjacent vertical surfaces of reactor cartridge 826. Inner gas permeablewall 836 is substantially cylindrical and defines a substantiallycylindrical gas withdrawal channel 818 which is in gaseous communicationwith gas space 844, which is provided below catalyst support plate 838and above upper tubesheet 855 of exchanger 840. Catalyst support plate838 extends to form a circumferential seal baffle 842 to prevent directgas flow between gas space 844 and gas distribution channel 821.

Reheat exchanger 840 is a baffled, tubular heat exchanger comprisingupper tubesheet 855, lower tubesheet 856, tubes 852 and baffles 853.Tubes 852 are adapted to receive gaseous effluent from first catalystbed 830 via gas space 844 and to pass said first catalyst bed effluentgas in indirect heat exchange with the product gases from secondcatalyst bed 890, as will be described in more detail below. The thuscooled first catalyst bed effluent gas is withdrawn from tubes 852 intoa lower gas space 857, which is positioned between tubesheet 856 andabove catalyst bed closure plate 891. Baffles 853 cause the secondcatalyst bed effluent gas to flow a tortuous path through exchanger 840for heating by said indirect heat exchange. The thus heated productgases are collected into a central gas space 846 for withdrawal vialongitudinal gas product tube passage 848 which comprises the inner gaspassage of product tube 801, positioned in the lower portion of reactorshell 834 for withdrawal of the product gases from the lower portion ofreactor 800.

Second catalyst bed 890 comprises upper closure plate 891, catalystsupport plate 892, outer cylindrical sheet 893, outer gas permeable wall866 and inner gas permeable wall 862. Walls 866 and 862 are secured tosupport plate 892. Cylindrical sheet 893 is positioned so as to definean annular gas space 860 between sheet 893 and the adjacent verticalsurfaces of reactor cartridge 826 and is provided with opening 868 forpassage of gases therethrough into a gas distribution channel 864 whichis defined by, and positioned between, the inner surface of sheet 893and outer gas permeable wall 866. An inner, annular-shaped gaswithdrawal channel 858 is provided between inner gas permeable wall 862and the outer surfaces 854 of product tube 801 for withdrawal of productgases from the second catalyst bed 890 upwardly to the shell side ofreheat exchanger 840.

In operation a first portion of the feed gases are introduced via feedtube 804 into upper gas space 822 and thence downwardly into annular gasdistribution channel 821 for inward, radial flow through first catalystbed 830. The product gases from first catalyst bed 830 are collected bygas withdrawal channel 818 and thence passed downwardly into gas space844 and tubes 852 of reheat exchanger 840 wherein these gases heat theproduct gases from second catalyst bed 890. The thus-cooled firstcatalyst bed effluent gas is collected into second gas space 857 andthen passed into annular gas space 860 for combination with the quenchstream prior to entry into second catalyst bed 890.

The second portion of the feed gas stream is introduced via feed tube802 and annular feed passage 806 into gas space 814 for passage toannular cooling channel 828 to provide the annular cooling of reactorshell 834. The thus-heated annular cooling gases are withdrawn fromchannel 828 into lower header space 876 and then passed upwardly throughgas passage 888 and lower gas space 880 as the quench stream to mix withand further cool the partially-cooled first bed product gas. Thecombined gas is passed through opening 868 in cylindrical sheet 893 asfeed to second catalyst bed 890. Product gases are withdrawn from secondbed 890 via gas withdrawal channel 858 and introduced to reheatexchanger 840 for heating as described above prior to withdrawal fromthe reactor via product tube 801.

Of course, FIG. 11 is not the only possible embodiment employing quenchfeed in combination with a reheat exchanger in accordance with theprocess and apparatus of this invention. Alternatives will be apparentto one skilled in the art from the above disclosure. For example, whilethe reheat exchanger in FIG. 11 is indicated as being positionedintermediate between the first and second catalyst beds, it is alsopossible to employ the reheat exchanger within one of the two catalystbeds (analogous to the positioning of exchanger 740 in bed 774 in theembodiment of FIG. 10). Thus, referring again to FIG. 9, elimination ofsecond exchanger 650 would mean that the partially cooled, firstcatalyst bed effluent gas withdrawn from reheat exchanger 640 could bepassed directly to gas distribution channel 652 for feed to secondcatalyst bed 672 after being admixed with the second portion of thefeedstream introduced to the reactor via conduit 666. In this embodimentof FIG. 9, stream 666 would constitute the quench feed.

Furthermore, it will also be apparent to one skilled in the art that themanner of introducing the various feedstreams and withdrawing theproduct stream from the reactor as illustrated in the foregoing figuresis not critical to the present invention. For example, it is notcritical that the feed conduit or product conduit be centrally locatedabout the longitudinal axis of the reactor, and each of these caninstead, if desired, be located off-center or located so as to introducethe gas feedstream into, and withdraw the product stream from, the sideof the reactor. In addition, the direction of flow of the gases throughthe reactor is not critical and the overall direction of flow of feedand product stream can either be countercurrent or cocurrent andpredominantly upflow, downflow, or horizontal. Obviously, therefore, thereactor of this invention can be positioned vertically as shown in theillustrations or horizontally or in any other desired manner.

The process and apparatus of this invention can be further illustratedby reference to the following examples.

COMPARATIVE EXAMPLES A AND B; EXAMPLE 1

A prior art two-bed ammonia converter 10 as illustrated in FIG. 1 havinginterbed heat exchanger 4 and lower heat exchanger 8 for cooling of thegas effluent from each bed by indirect heat exchange with a portion ofthe fresh ammonia syn gas feedstream 15, and having catalyst beds 2 and6 containing a defined volume of a prior art catalyst for ammoniasynthesis having a known catalyst activity (i.e., a "1x activity"catalyst) is configured for maximum waste heat recovery from reactoreffluent 9 by use of a stream generator 16 to produce a high-level steam(1425 psig) and a feed/effluent exchanger 14 (employing a closed by-passvalve 25) to preheat feed 12 to the desired reactor feed temperature,employing a syn gas feed of the selected composition, which is passed toreactor 10 at a selected pressure, temperature and flow rate (i.e.,space velocity).

The catalyst in each of beds 2 and 6 is replaced by an equal volume of aretrofit catalyst (i.e., the "3x activity" catalyst) having about threetimes the ammonia synthesis activity as the "1x activity" catalyst, andthe reactor 10 is again employed to produce ammonia. In view of thehigher activity of the retrofit catalyst, the synthesis gas compressor(not shown in FIG. 1) which supplies the synthesis gas feed can now berun at a lower speed, thereby requiring lower horsepower, to saveenergy. At the lower speeds, the reactor pressure is lowered and a lowerrate of the synthesis gas feed to the reactor results. However, sincethe more active catalyst yields a higher conversion per pass (i.e., ahigher ammonia content in the reactor effluent product gas) than the "1xactivity" catalyst, the amount of ammonia produced in moles per unittime can be maintained at the same level as is obtained when using the"1x activity" catalyst.

Set forth below in Table I are temperatures and other values which wouldbe obtained in use of the retrofitted "3x activity" catalyst in a priorart configuration as in FIG. 1 (Comparative Examples A and B).Comparative Example A only employs a high pressure steam generator.Comparative Example B seeks to obtain additional waste heat recovery byuse of a lower pressure steam generator in addition to the high pressuresteam generator employed in Comparative Example A.

In Example 1, an apparatus of this invention as illustrated in FIG. 2having a reheat exchanger 104 and a high pressure steam generator 122 isemployed under the conditions also summarized below in Table I, usingthe "3x activity" catalyst in the amounts and under the reactionconditions employed in Comparative Examples A and B.

It should be noted that in all of the cases listed in Table I, the bedinlet and outlet temperatures are equal. However, the reactor inlet andoutlet temperatures are substantially different. It should also be notedthat all three configurations achieve the same conversion of hydrogenand nitrogen to ammonia, that is all achieve the same outlet ammoniacomposition.

With the reduced circulation of synthesis gas which is possible in eachof these configurations using the "3x activity" catalyst, recovery ofall of the waste heat in the downstream 1425 psig boiler would requirean increase in the outlet temperature from the reactor (stream 9 inFIG. 1) since a lower flow rate carries a lower heat capacity andtherefore needs a larger temperature drop to transfer the same amount ofheat in steam generator 16. However, with a more active catalyst, thekinetically optimum reactor bed temperatures are lower. Thus, the outlettemperature from the second catalyst bed drops substantially with theretrofit of the "3x activity" catalyst. In an attempt to achieve thehigher desired reactor outlet temperatures, one can reduce the amount offeed preheating in the lower exchanger 8 of FIG. 1 until nearlycompletely by-passing this exchanger to make the reactor outlettemperature (stream 9) essentially equal to the outlet temperature ofthe second catalyst bed (stream 6b). However, this would still notachieve the objective of recovering all of the waste heat as 1425 psigsteam in boiler 16 because the stream 9 temperature would still be toolow.

Comparative Example A represents the situation in which excess heat,which is unable to be recovered in steam generator 16, is completelywasted. To avoid excessive feed preheating, the by-pass valve 25 on thefeed/effluent exchanger 14, must be opened, causing valuable waste heatto be thrown away to cooling water in downstream cooler 18. In thiscase, nearly 22 percent of the waste heat would be completely thrownaway.

In Comparative Example B, the effect is shown of the installation of a600 psig boiler 24, downstream of the 1425 psig steam generator 16, toassist in recovering waste heat. With the installation of the lowerpressure boiler 24, feed by-pass valve 25 could be kept closed. However,the 600 psig steam thus generated is less valuable than the 1425 psigsteam originally produced. Moreover, installation of this boilerrequires considerable investment for the boiler itself and for therequired piping modifications.

Use of the catalyst apparatus of this invention as in Example 1, whichemploys the same size catalyst beds as above in combination with reheatexchanger 104 and interbed exchanger 108 (replacing interbed exchanger 4and lower heat exchanger 8 of the prior art as shown in FIG. 1) resultsin a dramatic increase in the converter outlet temperature from 855° F.for Comparative Examples A and B, to 918° F. for Example 1. This highertemperature permits recovery of all of the waste heat as the morevaluable 1425 psig steam, and not only avoids the 22-percent loss ofwaste heat to cooling water, but also eliminates the investment for alower pressure boiler.

                                      TABLE I                                     __________________________________________________________________________                      Stream/                                                                             Comp.                                                                             Comp.                                                            FIG.                                                                             Apparatus                                                                           Ex. Ex.   Example                                     Stream/Device  No.                                                                              No.   A   B     1                                           __________________________________________________________________________    Preheated Syn Gas Feed (°F.)                                                          1  15    470 470                                                              2  115   --  --    533                                         Converter Inlet Pressure                                                                     1  15    2585                                                                              2585  --                                          (psia)         2  115   --  --    2585                                        Converter Feed Rate                                                                          1  15    89.7                                                                              89.7  --                                          (mol/hr) as percen-                                                                          2  115   --  --    89.7                                        tage of "1× activity"                                                   catalyst Feed Rate                                                            First Bed Feed (°F.)                                                                  1  2a    719 719   --                                                         2  121   --  --    719                                         First Bed Effluent (°F.)                                                              1  2b    949 949   --                                                         2  103   --  --    949                                         Second Bed Feed (°F.)                                                                 1  6a    708 708   --                                                         2  109   --  --    708                                         Second Bed Effluent (°F.)                                                             1  6b    858 858   --                                                         2  107   --  --    858                                         Converter Outlet NH.sub.3                                                                    1  9     18.54                                                                             18.54 --                                          Mole Percent   2  124   --  --    18.54                                       Ammonia Product (°F.)                                                                 1  9     855 855   --                                                         2  124   --  --    918                                         High Pressure Boiler                                                                         1  13    593 593   --                                          Effluent (°F.)                                                                        2  122   --  --    594                                         Low Pressure Boiler                                                                          1  24    --  521   --                                          Effluent (°F.)                                                                        2  128   --  --    --                                          Feed Effluent Exchanger                                                                      1  17    241 166   --                                          Outlet (°F.)                                                                          2  117   --  --    173                                         Bypass Valve Setting                                                                         1  25    OPEN                                                                              CLOSED                                                                              --                                                         2  125   --  --    CLOSED                                      Percentage of Waste     22.0                                                                              --    --                                          Heat Lost to Cooling                                                          Water                                                                         Percentage of Waste Heat                                                                              --  22.0  --                                          Degraded from 1425                                                            psig steam to 600                                                             psig steam                                                                    __________________________________________________________________________

COMPARATIVE EXAMPLES C AND D AND EXAMPLES 2-3

These examples illustrate the improvement achieved by the use of theprocess and apparatus of this invention by the retrofit of a still moreactive catalyst (herein termed the "6x activity" catalyst) having aboutdouble the activity for ammonia synthesis of the "3x activity" catalystemployed in Example 1 and Comparative Examples A and B above. The "6xactivity" catalyst therefore has approximately 6 times the activity ofthe "1x activity" catalyst. With this higher activity catalyst, an evenlarger reduction in syn gas compressor speed is possible compared tothat which is used above for the "3x activity" catalyst.Correspondingly, the pressure and reactor feed flow rate will bedecreased. Also, the kinetically optimum second bed outlet temperature,and therefore the prior art converter outlet temperature, are furtherreduced. This makes heat recovery from the converter effluent streamusing prior art apparatus as in FIG. 1, even more difficult.

Comparative Examples C and D in Table II correspond to ComparativeExamples A and B discussed above. Therefore, Comparative Example Ccorresponds to the retrofit of the 6x activity catalyst into anapparatus of FIG. 1 in which a 1425 psig steam generator 16 is used, andComparative Example C adds a 600 psig steam generator 24. Example 2corresponds to the apparatus of FIG. 2 as configured for Example 1above, and employs a 1425 psig steam generator 122. The additionalexample, namely example 3, corresponds to the apparatus as configuredfor Example 2, except that a 600 psig steam generator 128 is alsoemployed to receive the partially cooled ammonia product gas effluentwithdrawn from the 1425 psig steam generator 122 for further heatrecovery.

From Table II, it can be seen that the converter outlet temperatureusing the prior art configurations in Comparative Examples C and D,which employed an interbed and lower heat exchanger, drops from 855° to825° F., which severely reduces the ability to recover convertereffluent waste heat. In fact, based on Comparative Example C, nearly 38percent of the available waste heat is lost to cooling water (i.e.,exchanger 14 by-pass valve 25 is in the open position). For ComparativeExample D, the installation of the 600 psig boiler 24 reduces this lossto 17 percent. However, the incremental 21 percent recovered heat isdowngraded from the higher value 1425 psig level to the less valuable600 psig level.

Example 2, using the reheat basket of this invention in which a reheatexchanger 104 is employed, results in a 21-percent loss of convertereffluent waste heat to cooling water. However, all of the waste heatthat is recovered in boiler 122 is used for generating the more valuable1425 psig steam, and the heat recovery is much greater than in the caseof Comparative Example C.

Example 3, which employs a reheat exchanger 104 in combination with theadditional use of 600 psig steam generator downstream of the 1425 psigsteam generator 122, permits the recovery of all the waste heat,although 21 percent has been downgraded to the less valuable 600 psiglevel. In contrast, Comparative Example D is unable to recover all ofthe converter waste heat even in a train in which a 1425 boiler 16 and600 psig boiler 24 is used, and 17 percent of the waste heat is lost tocooling water in Comparative Example D.

Therefore, the apparatus of this invention permits higher converteroutlet temperatures which enhance the recovery of converter effluentwaste heat for high pressure steam generation.

                                      TABLE II                                    __________________________________________________________________________                     Stream/                                                                             Comp.                                                                             Comp.                                                            FIG.                                                                             Apparatus                                                                           Ex. Ex. Example                                                                            Example                                   Stream/Device No.                                                                              No.   C   D   2    3                                         __________________________________________________________________________    Preheated Syn Gas Feed                                                                      1  15    400 400 --   --                                        (°F.)  2  115   --  --  463  463                                       Converter Inlet Pressure                                                                    1  15    2360                                                                              2360                                                                              --   --                                        (psia)        2  115   --  --  2360 2360                                      Converter Feed Rate (mol/                                                                   1  15    81.5                                                                              81.5                                                                              --   --                                        hr) as Percentage of                                                                        2  115   --  --  81.5 81.5                                      "1× Activity" Cata-                                                     lyst Feed Rate                                                                First Bed Feed (°F.)                                                                 1  2a    660 660 --   --                                                      2  121   --  --  660  660                                       First Bed Effluent (°F.)                                                             1  2b    918 918 --   --                                                      2  103   --  --  918  918                                       Second Bed Feed (°F.)                                                                1  6a    708 708 --   --                                                      2  109   --  --  708  708                                       Second Bed Effluent                                                                         1  6b    826 826 --   --                                        (°F.)  2  107   --  --  826  826                                       Converter Outlet NH.sub.3                                                                   1  9     20.0                                                                              20.0                                                                              --   --                                        Mole Percent  2  124   --  --  20.0 20.0                                      Ammonia Product (°F.)                                                                1  9     825 825 --   --                                                      2  124   --  --  888  888                                       High Pressure Boiler                                                                        1  13    592 592 --   --                                        Effluent (°F.)                                                                       2  122   --  --  593  593                                       Low Pressure Boiler                                                                         1  24    --  510 --   --                                        Effluent (°F.)                                                                       2  128   --  --  --   510                                       Feed Effluent Exchanger                                                                     1  17    308 226 --   --                                        Outlet (°F.)                                                                         2  117   --  --  242  166                                       Bypass Valve Setting                                                                        1  25    OPEN                                                                              OPEN                                                                              --   --                                                      2  125   --  --  OPEN CLOSED                                    Percentage of Waste    38.0                                                                              17.0                                                                              21.0 --                                        Heat Lost to Cooling                                                          Water                                                                         Percentage of Waste Heat                                                                             --  21.0                                                                              --   21.0                                      Degraded from 1425                                                            psig steam to 600                                                             psig steam                                                                    __________________________________________________________________________

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and withoutdeparting from the spirit and scope thereof can make various changesand/or modifications to the invention for adapting it to various usagesand conditions. Accordingly, such changes and modifications are properlyintended to be within the full range of equivalents of the followingclaims.

What is claimed is:
 1. In an exothermic catalytic reactor having atleast two catalytic beds arranged for sequential gas flow therethrough;gas supply means for introducing a gas feedstream to the first of saidcatalyst beds for partial reaction of said gas feedstream therein;interbed gas cooling means for cooling the gas effluent from eachcatalyst bed to remove heat therefrom prior to passing said gas effluentto the next of said sequentially arranged catalyst beds and means forremoving a gaseous effluent from the last of such catalyst reactor bedsas said gas product, the improvement wherein said reactor additionallycomprises reheat exchange means constructed and arranged for heating atleast a portion of said last catalyst bed effluent gas by indirect heatexchange with a heating fluid comprising at least a portion of thegaseous efflunt from at least one other of said reactor beds prior towithdrawal of said product gas from said reactor.
 2. The improvedexothermic catalytic reactor of claim 1 wherein each said catalyst bedis arranged for radial flow of gases therethrough.
 3. In an exothermiccatalytic reactor having at least two catalytic reactor beds arrangedfor sequential flow of a gas therethrough and for partial reaction ofsaid gas in each said catalytic reactor bed; having gas supply means forintroducing a gas feedstream to the uppermost upstream catalytic reactorbed; having means for feeding a gas effluent from each sequentiallynon-terminal said catalytic reactor beds as a gas feed to eachsequentially next said catalytic reactor bed; having interbed coolingmeans for cooling said gas effluent from each catalytic reactor bed toremove heat therefrom prior to passing said gas effluent to thesequentially next said catalytic reactor bed; and having means forremoving said gaesous effluent from the sequentially last of saidcatalytic reactor beds as a gas product, the improvement wherein saidreactor additionally comprises at least one effective reheat exchangemeans constructed and arranged for recovering excess or waste heatwhereby at least a portion of said gas product is heated by indirectheat exchange with a heating fluid comprising at least a portion of saidgas effluent from at least one other of said catalytic reactor bedsprior to withdrawal of said product gas from said reactor.
 4. In anexothermic catalytic reactor having at least two catalytic reactor bedsarranged for sequential flow of a gas therethrough and for partialreaction of said gas therein; having gas supply means for introducing agas feedstream to the uppermost upstream said catalytic reactor bed;having means for feeding a gas effluent from each sequentiallynon-terminal said catalytic reactor bed as a gas feed to eachsequentially next said catalytic reactor bed; having interbed gascooling means for cooling said gas effluent from each catalytic reactorbed to remove heat therefrom prior to passing said gas effluent to thesequentially next said catalytic reactor bed; and having means forremoving said gas effluent from the sequentially terminal said catalyticreactor bed as a gas product, the improvement wherein said reactoradditionally comprises at least one effective reheat exchange meansconstructed and arranged for optimizing thermo-kinetically saidexothermic catalytic reactor whereby at least a portion of said gaseffluent from said last catalytic reactor bed is heated by indirect heatexchange with a heating fluid comprising at least a portion of said gaseffluent from at least one other of said catalytic reactor beds prior towithdrawal of said product gas from said reactor.
 5. In an exothermiccatalytic reactor having at least two catalytic reactor beds arrangedfor sequential flow of a gas therethrough and for partial reaction ofsaid gas therein; having gas supply means for introducing a gasfeedstream to said catalytic reactor bed which is uppermost upstream;having means for feeding a gas effluent from each sequentiallynon-terminal said catalytic reactor bed as a gas feed to eachsequentially next catalytic reactor bed; having interbed gas coolingmeans for cooling said gas effluent from each said catalytic reactor bedto remove heat therefrom prior to passing said gas effluent to thesequentially next said catalytic reactor bed; and having means forremoving said gas effluent from the sequentially terminal said catalyticreactor bed as a gas product, the improvement wherein said reactoradditionally comprises at least one effective reheat exchange meansconstructed and arranged for recovering excess or waste heat and foroptimizing thermo-kinetically said exothermic catalytic reactor wherebyat least a portion of said gas effluent from last said catalytic reactorbed is heated by indirect heat exchange with a heating fluid comprisingat least a portion of said gas effluent from at least one other of saidcatalytic reactor beds prior to withdrawal of said gas product from saidexothermic catalytic reactor.
 6. The improved exothermic catalyticreactor of claim 3, 4 or 5 wherein each said catalyst bed is arrangedfor radial flow of gases there through.